The present invention relates generally to communications buoys and communications systems that utilize such buoys, and more particularly to a high frequency (HF) surface to surface communications buoy that employs spread spectrum modulation.
Conventional communications buoys, commonly known as sonobuoys, utilize ultra high frequency (UHF) radio communications. One current UHF sonobuoy system is manufactured by Magnavox. Such UHF communications sonobuoys are limited to line of sight communications paths between the sonobuoy transmitter and a receiver platform, such as a ship or an aircraft. Such conventional sonobuoy links require an airborne relay between the transceiver and the distant terminal. Typically, an aircraft flies in the vicinity of the buoy and relays messages transmitted by the buoy to remote locations. As such, conventional sonobuoy systems do not permit their use in networked, multiple hop relay systems, for example.
In addition, a number of U.S. Patents disclose technology relating to buoy communications systems, line of sight HF communications systems and spread spectrum communications systems. The following are illustrative of conventional systems.
U.S. Pat. No. 4,336,537 for "Bi-Directional Underwater Communication System," issued to Strickland discloses a system wherein a submerged operator can communicate with a surface site. The operator uses a face-mask-mounted microphone and an earphone connected to a submerged watertight radio. An antenna is carried by a buoy to the surface of the body of water in which the operator is submerged to provide a communication path for the operator. The submerged radio is disclosed to be a PRC-77 radio, which operates in the 2-70 MHZ band, which encompasses the HF bandwidth utilized in the present invention. However, nothing whatsoever is disclosed regarding the operation of the radio, including either surface wave or sky wave propagation modes, or of the use of spread spectrum encoding of the HF signals. This patent discloses a line of sight communications system which permits communication from the submerged operator to a vessel on the surface, or a surface control craft, for example.
U.S. Pat. No. 4,203,109 for "Submarine Communication System," issued to Ballard et al discloses a method and apparatus for communicating information between a submerged vessel and an aircraft, for example. The communications is achieved by means of an expendable cable link between the vessel and the surface. A buoy is attached to the cable link and contains a transmitter and a receiver which is released from the submerged vessel and floats on the surface. The cable link provides electrical and power leads between the submerged vessel and the buoy. The communications is accomplished by conventional RF radio transmissions. Nothing whatsoever is disclosed in this patent regarding the use of HF sky wave or surface wave propagation or the use of spread spectrum encoding of the HF signals.
U.S. Pat. No. 3,946,391 for "Buoy Antenna System," issued to Cuckler et al discloses an expendable marker buoy which includes an RF transmitter and antenna arrangement enclosed within the buoy enclosure. The design is such that a antenna is coupled by way of a dielectric material to the water which acts as a ground plane for the antenna.
U.S. Pat. No. 4,203,160 for "Submarine Communication," issued to Doherty discloses a communication system wherein a very low frequency (VLF) communication link is established between a relay ship or a relay drone, and from the ship or drone to a submarine by way of an acoustic link. Mention is made that communications can be made by way of an RF, MF, HF or UHF communication link employed at the relay station or in the drone. However, no description of the particular equipment or operation of HF equipment is disclosed. In addition, there is no mention of HF surface wave or sky wave propagation or the use of spread spectrum encoding of HF signals.
U.S. Pat. No. 4,639,900 entitled "Method and a System for Monitoring a Sea Area," issued to Gustafson, discloses a system wherein listening devices are employed to monitor the sea area. Transmitters coupled to the listening device utilize channelized HF to communicate to master monitoring station. His communication system employs direct line of sight HF communications and nothing is disclosed or suggested regarding the use of surface or sky wave propagation or spread spectrum modulation.
U.S. Pat. No. 4,291,409 entitled "Spread Spectrum Communications Method and Apparatus," issued to Weinberg et al, discloses a wide bandwidth communications system employing spread spectrum techniques. Buoy transmitters are employed in a direct line of sight communications link to synchronously orbiting satellites. The satellites relay the transmitted information to a base station located on land. As in the previously discussed patents, nothing is disclosed regarding the use of HF surface or sky wave communications or the combining of spread spectrum techniques with such HF surface or sky wave communications equipment.